I have a Thermo Pride WC-27 wood furnace and I'm new to wood furnaces and my furnace has a thermo-disc (snap disc) and a fan/limit control wired into the thermostat. Is this a normal set-up, or should it have one or the other? The fan/limit switch seems to be the one that is turning on my blower, but I don't know if the snap disc has any purpose wired with it.